Posted by Kasra Hassani
The differentiation of the promastigote Leishmania to the amastigote form is one of the most interesting and promising areas of study in Leishmania research. Researchers are interested to know what are the differences between these two life-stages, how do the parasites shift from one to the other and what happens during this transformation. Rosenzweig et al. have addressed these questions by proteomic comparison of Leishmania donovani’s proteome during its transformation from the promastigote to the amastigote form. Using a new labelling method called the iTRAQ, they have looked at the proteome of L. donovani after stimulation with low pH and high temperature within 2.5, 5, 10, 15, 24h and after 6 days. With their method they believe that they have been able to detect half of the parasite’s proteome. This study has shown key changes in the proteome content of L. donovani which corresponds with its metabolic needs in the phagolysosome.
The mid-gut of sandfly is a sugar-rich environment because of its nectar-diet supplemented with occasional bloodmeals. However, sugars are scarce in the phagolysosome and the parasite has to switch to fatty acids and amino acids as energy sources. According to Rosenzweig et al., starting from 10h after stimulation, glycolysis enzymes are down-regulated while enzymes required for beta-oxidation, gluconeogenesis, amino acid catabolism, TCA cycle and mitochondrial respiration are up-regulated. Furthermore, protein translation and thus metabolism slows down which corresponds to parasite’s smaller size and slower growth. In this way the parasite retools its metabolism to be able to live and multiply inside the phagolysosome. Another interesting and rather surprising finding of Rosenzweig et al. is that most of these alterations in metabolism start rather late (after 10-15h) and they take hours to maturate. This finding, raises the question that how do incompletely differentiated parasites reside in the same host environment as the mature amastigotes?